Oil prices often fluctuate on basic supply and demand principles, but one CEO says the weak dollar is to credit for recent gains.

This morning, Exxon Mobil (NYSE: XOM - News) CEO Rex Tillerson told CNBC that the weak dollar is contributing about $20 to $25 a barrel to crude oil's pricing. He explained that while inventory levels are at historic highs, the "foreign exchange effect" is supporting the price.

Should Tillerson's calculations prove accurate, oil-tied equities could get hammered when the Fed decides to lift interest rates from near zero. While Bernanke and company have pledged to keep rates where they are for an extended period, investors should be wary of prospects related to an inevitable rate hike.

Energy trusts are among the equity plays that could potentially be punished by a dollar rebound. The Canadian Energy Trusts Index is one of the top-10 performing tickerspy Indexes over the last month, with select players rising by double-digit percentages.

Harvest Energy Trust (NYSE: HTE - News) is up by more than 37% in the last month, after reports that South Korea's state-owned National Oil Corp would buy the company for $3.9 billion.

Meanwhile, sizable runs by Enterra Energy Trust (NYSE: ENT - News), Penn West Entergy Trust (NYSE: PWE - News), and Provident Energy Trust (NYSE: PVX - News) could all be erased by a dollar rally.

Precision Drilling Trust (NYSE: PDS - News), Enerplus Resources Fund (NYSE: ERF - News), and Pengrowth Energy Trust (NYSE: PGH - News) are already negative on a one-month basis. A further pullback by oil prices would most likely extend their declines, offering more attractive entry points.

The Canadian Energy Trusts Index is consistently among tickerspy's top Indexes ranked by dividend yield, and as such the stocks remain solid long-term plays. However, dollar-driven oil prices don't have the stability of strong fundamentals, and that could lead to further volatility in the sector and opportunities to buy on the dips.

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